1. Field of the Invention
The present invention relates to what is called an FIMS system (front-opening interface mechanical standard system) (or load port) that is used in semiconductor manufacturing process, upon transferring a wafer(s) stored in a transport container called a pod into a semiconductor processing apparatus, as a structure on which the pod is placed. More particularly, the present invention relates to components related to an FIMS system on which a pod (one referred to as an FOUP (front-opening unified pod)) is placed and that transfers a semiconductor wafer(s) from the pod, namely a pod clamping unit for fixing a pod on the FIMS system, a load port on which a pod compatible with that clamping unit is to be placed, and a mini-environment system including a pod and a load port that are compatible with that clamping unit.
2. Related Background Art
In the past, the semiconductor manufacturing process had been performed in what is called a clean room constructed by establishing a high degree of cleanness in the room in which semiconductor wafers are handled. In recent years, however, in view of an increase in the wafer size and with a view to reduce cost incurred in maintenance of the clean room, a method of keeping clean only the interior of a processing apparatus, a pod (or wafer container) and a small space through which substrates or wafers are transferred between the pod and the processing apparatus has been used.
The pod is composed of a body portion of a substantially cubical shape having shelves provided therein that can hold a plurality of wafers in a parallel and separated state and an opening provided on one side thereof through which wafers can be brought into/out of it, and a lid for closing the opening. Those pods which have an opening portion provided not on the bottom but on one lateral side thereof (i.e. the front side to be opposed to the small space) are collectively called FOUP (front-opening unified pod). The present invention is directed to technologies in which the FOUP is used.
A system provided with the above mentioned small space has a first opening opposed to the opening of the pod, a first door for closing the first opening, a second opening provided on a semiconductor processing apparatus, and a transferring robot that is adapted to reach into the interior of the pod through the first opening to pick up a wafer and transfer it into the processing apparatus through the second opening. The system provided with the small space also has a support table that supports the pod in such a way that the pod opening is placed just in front of the door.
On the top face of the support table are positioning pins to be fitted into positioning holes provided on the bottom surface of the pod and a clamp portion adapted to engage with a portion to be clamped provided on the bottom surface of the pod to fix the pod to the support table. Typically, the support table is adapted to be movable toward and away from the door over a predetermined distance. When the wafers in a pod are to be transferred into the semiconductor processing apparatus, the support table on which the pod is placed moves toward the door until the lid of the pod abuts the door, and then after abutment, the lid is removed by the door, whereby the opening of the pod is opened. By this process, the interior of the pod and the interior of the processing apparatus are brought into communication with each other through the small space to allow wafer transferring operations that will be performed repeatedly. All of the support table, the door, the first opening, a mechanism for opening/closing the door and walls partly defining the small space and having the first opening are included in what is referred to as an FIMS system (front-opening interface system) or a mini-environment system.
A clamping mechanism used in the FIMS system is composed of an engagement recess provided on the bottom surface of the pod and a clamp portion provided on the support table. The engagement recess has a portion to be clamped extending toward the center of the recess to cover a part of the opening of the recess. A known conventional clamping mechanism is disclosed in Japanese Patent Application Laid-Open No. 2002-164412 (which will be referred to as patent document 1 hereinafter). The clamp portion 503 disclosed in patent document 1 is of what is called a front-retaining type. As shown in FIG. 9, the clamp portion 503 used in the front-retaining system is a substantially rod-like member that is supported in a swingable manner. The clamp portion 503 has a hook claw 504 provided at a first end thereof, and the second end thereof is connected to an actuator 540. In this structure, the actuator 540 drives the second end of the clamp portion 503 to cause the clamp portion 503 to swing, whereby the hook claw 504 is brought into engagement with the portion to be clamped 533 provided on the pod 506. Thus, dislocation of the pod 506 from the support table 519 is prevented.
In the system disclosed in patent document 1 in which the pod 506 is secured on the support table 519 only by front retaining, if the pod 519 is displaced (as shown by the broken lines) by an excessive external force acting on the pod 519 in the obliquely upward direction (indicated by arrow z in FIG. 9), there is a risk that the clamp portion 504 and the portion to be clamped 533 may be disengaged and the pod 506 may be dislocated from the support table 519 inadvertently.
Furthermore, with an increase in the weight of the pod accompanied by an increase in the size thereof, a load generated by inertia upon moving the pod and an impact force that may be caused upon transferring a wafer also becomes larger. In such cases, the fastening ability of conventional clamp units is relatively low, and the position of the pod may be displaced and the pod may be dislocated by a load that acts on the pod upon movement of the pod or other occasions.
In a known conventional structure, positioning pins are provided on the upper surface of the support table in such a way as to project therefrom, and positioning holes complementary to the positioning pins are provided on the bottom surface of the pod so that positioning pins are fitted into the positioning holes when the pod is placed on the support table. However, the diameter of the opening of the positioning hole is larger than the diameter of the positioning pin, and the cavity of the positioning hole is countersunk (i.e. the wall of the cavity is slanted toward the center of the hole) so that the positioning pins of the pod can slide into the corresponding positioning holes. Since the circumferential wall of the positioning hole is slanted, when a load is applied in an oblique direction, the positioning pins and the positioning holes are easily disengaged. Therefore, it is difficult to keep the pod in the fixed state.
Furthermore, in the case of positioning pins in the form of projections having a triangular cross section, a SEMI standard requires that the positioning pins can fit into the positioning holes even when the pod is placed with a misalignment of about ±10 mm relative to the positioning holes. Accordingly, they do not function effectively in keeping the pod fixed.